Carnivore trees are a type of tree that lives in Forest. According to Septimus Heap, they capture their victim by their branches and then they eat everything from victim, until there is just skeleton left behind. Skeleton can seem sitting on the brances. It appears they hunt in night.
Septimus and Nicko Heap were searching for Jenna from the Forest when Septimus shared the information he learned during his Young Army days. The boys initially mistook Benjamin Heap as a Carnivore tree.